Police were called to the shopping centre just before 8pm last night to reports a boy was approached with a group of people who threatened him with a knife.
Two boys and a man were arrested near to Chafford Hundred train station while officers seized an imitation firearm and a knife.
An 18-year-old man from Romford and a 17-year-old boy from Dagenham were arrested on suspicion of robbery, possession of firearms offences and possession of a knife.
Police also arrested a 15-year-old boy from Rainham on suspicion of robbery.
They all remain in custody for questioning.
Tags: Grays, Thurrock, Romford, Lakeside, Dagenham, Rainham